Variable resistance memory stack with treated sidewalls

ABSTRACT

Memory devices and methods for fabricating memory devices have been disclosed. One such method includes forming a memory stack out of a plurality of elements. A sidewall liner is formed on a sidewall of the memory stack using a physical vapor deposition (PVD) process, including an adhesion species and a dielectric, such that the adhesion species intermixes with an element of the memory stack to terminate unsatisfied atomic bonds of the element and the dielectric forms a dielectric film with the adhesive species on the sidewall.

PRIORITY APPLICATION

This application is a divisional of U.S. application Ser. No.14/266,456, filed Apr. 30, 2014, which is incorporated herein byreference in its entirety.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits in apparatuses such as computers or other electronicdevices. There are many different types of memory includingrandom-access memory (RAM), read only memory (ROM), dynamic randomaccess memory (DRAM), synchronous dynamic random access memory (SDRAM),and non-volatile (e.g., phase change memory, flash) memory.

Non-volatile memories are important elements of integrated circuits dueto their ability to maintain data absent a power supply. Phase changematerials have been investigated for use in non-volatile memory cells.Phase change memory (PCM) elements include phase change materials, suchas chalcogenide alloys, that are capable of stably transitioning betweenamorphous and crystalline phases. Each phase exhibits a particularresistance state and the resistance states distinguish the logic valuesof the memory element. Specifically, an amorphous state exhibits arelatively high resistance and a crystalline state exhibits a relativelylow resistance. One of different logic levels (e.g., logic 1 or logic 0)can be assigned to each of these states.

There are general needs to improve PCM devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a typical phase changememory stack.

FIGS. 2-7 illustrate an embodiment of a process flow to fabricate aphase change memory stack having treated sidewalls.

FIG. 8 illustrates an embodiment of a radio frequency physical vapordeposition process.

FIG. 9 illustrates a block diagram of a memory system in accordance withthe embodiments of FIGS. 2-7.

DETAILED DESCRIPTION

As described subsequently, a method for fabricating a memory stack(e.g., memory device) with treated sidewalls can increase the adhesionof dielectric passivation material to the electrodes. This can reduceinter-diffusion between the electrodes and adjacent materials in thememory stack.

FIG. 1 illustrates a typical memory cell stack for a PCM. Carbon can beused as top 101, middle 102, and bottom 103 electrodes for the memorycell stack. Carbon is chemically inert and does not react easily withthe phase change material 110 or the selector device material 111. Thisinert chemistry can also lead to poor adhesion of sidewalls to thecarbon electrodes. As a result, it can be possible for the sidewallmaterial 120, 121 to inter-diffuse 130, 131 between the selector devicematerial 111 and the phase change material 110. This can occur at highertemperatures. The inter-diffusion can cause reliability issues, degradeleakage current, and affect threshold voltage stability.

FIGS. 2-7 illustrate various steps in fabricating a memory stack (e.g.,phase change memory (PCM)) in addition to treating the sidewalls of thememory stack with an adhesion species. These fabrication steps are forpurposes of illustration only as the different elements of the stack canbe formed by different processes.

FIG. 2 illustrates an embodiment of a blanket deposition of the initialmemory stack material 200. The memory stack can include a word linematerial (e.g., tungsten (W)) 201. A first electrode material 202 (e.g.,carbon) can be formed on the word line material 201. A selector devicematerial 203 may be formed on the first electrode material 202.

The selector device material 203 (SD) may include Selenium (Se), Arsenic(As), Germanium (Ge), Tin (Sn), Tellurium (Te), Silicon (Si), Lead (Pb),Carbon (C), or Bismuth (Bi) as well as other materials. Otherembodiments can include selector device material 203 comprising one ormore of these elements as well as one or more of these elements combinedwith other elements.

A second electrode material 204 (e.g., carbon) can be formed on theselector device material 203. A phase change material 205 can be formedon the second electrode material 204.

The phase change material 205 (PM) can include chalcogenide elementssuch as Germanium (Ge), Antimony (Sb), Tellurium (Te), Indium (In) aswell as other chalcogenide elements, combinations of these elements, orcombinations of these elements with other elements. The phase changematerial 205 can additionally include Aluminum (Al), Gallium (Ga), Tin(Sn), Bismuth (Bi), Sulphur (S), Oxygen (O), Gold (Au). Palladium (Pd),Copper (Cu), Cobalt (Co), Silver (Ag), or Platinum (Pt) as well as otherelements. Additional embodiments can combine these elements with thechalcogenide elements.

A third electrode material 206 (e.g., carbon) can be formed on the phasechange material 205. Forming the third electrode material 206, as wellas the other materials 201-205 of the memory stack, can be done with ablanket deposition method or some other deposition method.

After the initial memory stack material 200 has been formed, an etchprocess (e.g., dry etch) can be performed on the stack material 200 tocreate trenches 301-304 as illustrated in FIG. 3. FIG. 3 illustratesthat the stack material 200 has been divided by the plurality oftrenches 301-304 into a plurality of memory stacks 311-315, each stackcomprising the architecture illustrated in FIG. 2.

In another embodiment, the stack material 200 can be dry etchedpatterned in both x and y directions. Thus, subsequent sidewall linerscan be added on four sidewalls, as illustrated in FIG. 7.

FIG. 4 illustrates the treatment of the sidewalls to form sidewallliners (as seen in FIG. 5) on the stacks 311-315 as formed in theembodiment illustrated in FIG. 3. A radio frequency (RF) physical vapordeposition (PVD) process, illustrated in greater detail in FIG. 8, canbe used to form an adhesion species 401, 402 on the stack sidewalls.This treatment can enhance the dielectric liner adhesion to theelectrode surfaces.

The stack sidewalls can be treated with the adhesion species 400 (e.g.,boron) by exposing the sidewalls to the adhesion species and dielectricmaterial (e.g., boron nitride (BN_(X))) in a PVD chamber. Boron hasproperties that are between metals and non-metals. It is a semiconductorrather than a metallic conductor. Other adhesion species 401-403 thathave substantially similar properties can also be used.

FIG. 8 illustrates an embodiment of an RF PVD process. The memory device800 is placed in the PVD chamber 801 along with a target 810 of boron(B) or BN_(X). A magnetron 820, using an RF source 830 (e.g., 1 kilowatt(kW) at 40 megahertz (MHz)) has a higher frequency as compared to asubstrate bias 805 (e.g., 300 Watts, 13.56 MHz) of the memory device.The magnetron can also have a direct current (DC) power source. The PVDchamber can have a relatively high pressure (e.g., 50-150 milliTorr(mT)). The combination of relatively high pressure, relatively high RFfrequency, and the substrate bias can result in increased scattering,increased ionization, increased re-sputtering that can result in arelatively dense/high aspect ratio structured sidewall 401, 402 ascompared to other deposition processes.

If a target 810 of BN_(X) is used, an argon (Ar) plasma 803 can beformed in the PVD chamber 801. If a target 810 of boron is used (e.g.,reactively sputtered), a plasma 803 of Ar+N₂ gas mixture can be used. Insuch an embodiment, the adhesive species (e.g., boron) can be implantedat the electrode/liner interface 430 (see FIG. 4) and the dielectricmaterial (e.g., N₂) can form a film with the adhesive species. WhileBN_(X) is used for purposes of illustration, the present embodiments arenot limited to any one adhesion species or dielectric material.

Referring to the more detailed view 420 of FIG. 4, the RF PVD processcan form a sidewall liner 402 on one or more of the electrodes 410. Theenergetic nature of the PVD process can enhance sidewall liner adhesionwith ion impingement. The C—B bonds 430 can create a stable, adhesiveinterface between the liner 402 and the electrode 410 when the adhesivespecies intermixes with an element of the electrode to terminateunsatisfied atomic bonds of the electrode. The PVD process can alsoprovide a more controlled deposition process for form a relatively densesidewall liner 402. While the detail 420 of FIG. 4 focuses on the secondelectrode 410, the present embodiments can perform substantially similarresults on the other electrodes as well as other elements of the stack.

FIG. 5 illustrates the stacks 311-315 as a result of forming thesidewall liners 500-508 on the sidewalls of the stacks 311-315 as seenin FIGS. 4 and 8. The process to form the sidewall liners 500-508 cancomprise any adhesive species or dielectric material. For purposes ofillustration, a dielectric material like AlSiO_(x) can be used.

FIG. 6 illustrates an embodiment for forming a dielectric fill material601-604 between adjacent memory stacks. The dielectric fill material601-604 can electrically isolate each of the memory stacks. Thedielectric fill material 601-604 can be the same material as thesidewall liners 500-508 or a different dielectric material.

FIG. 7 illustrates an embodiment for forming additional decks of memorystacks. For example, FIG. 7 shows two memory stacks 701, 702 coupledtogether at a common bit line 703. The sidewalls or the sidewall linertreatment described previously with reference to FIGS. 4 and 8 may berepeated for the memory stacks at each of the decks. Other embodimentscan have additional decks of memory stacks 701, 702.

The represented sequence of layers is for purposes of illustration only.Other embodiments can use other sequences. For example, the relativeposition of the PM and select material (SD) may be exchanged. Also, therelative positions of word line material and bit line material may bechanged (e.g., having bit lines at the bottom of the first deck and wordlines at the top of the first deck and possibly shared with a seconddeck stack.

FIG. 9 illustrates a block diagram of a memory system that include amemory device 901 that can use the memory stacks with treated sidewallsof FIGS. 2-7. A controller 900 may be used to control operations of thesystem. The memory device 901, coupled to the controller 900, mayinclude a memory array comprising memory cell stacks as described abovewith reference to FIGS. 2-7.

The controller 900 may be coupled to the memory device 901 over control,data, and address buses. In another embodiment, the address and databuses may share a common input/output (I/O) bus. The controller 900 canbe part of the same integrated circuit as the memory device 901 or asseparate integrated circuits.

As used herein, an apparatus may refer to, for example, circuitry, anintegrated circuit die, a memory device, a memory array, or a systemincluding such a circuit, die, device or array.

CONCLUSION

One or more embodiments of the method for memory stack sidewalltreatment can result in a memory device with memory stacks havingenhanced adhesion between the sidewall liners and the memory stack. Forexample, an RF PVD process can be used to deposit a sidewall linercomprising an adhesion species and a dielectric material (e.g., BN_(X)).The adhesion species (e.g., boron) can form a bond (e.g., B—C) with anelement (e.g., carbon) of the electrodes in order to create an enhancedadhesion between the sidewall liners and the memory stack. In such anembodiment, the adhesion species intermixes with an element of thememory stack to terminate unsatisfied atomic bonds of that element.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations willbe apparent to those of ordinary skill in the art. Accordingly, thisapplication is intended to cover any adaptations or variations.

1. A memory system comprising: a controller to control the system; and amemory device, coupled to the controller, the memory device comprising:a memory stack defined in part by sidewalls, comprising: a first carbonelectrode; a selector device over the first carbon electrode; a secondcarbon electrode over the selector device; a phase change material overthe second carbon electrode; and a third carbon electrode over the phasechange material; and a sidewall liner material on sidewalls of thememory stack wherein the sidewall liner comprises a physical vapordeposited BN_(X) such that the boron is configured to intermix with thecarbon of the electrodes at an interface of the sidewall liner materialand the sidewalls.
 2. The memory system of claim 1, wherein the selectordevice comprises one or more of Selenium (Se), Arsenic (As), Germanium(Ge), Tin (Sn), Tellurium (Te), Silicon (Si), Lead (Pb), Carbon (C),and/or Bismuth (Bi).
 3. The memory system of claim 1, wherein the phasechange material comprises one or more of Germanium (Ge), Antimony (Sb),Tellurium (Te), Indium (In), Aluminum (Al), Gallium (Ga), Tin (Sn),Bismuth (Bi), Sulphur (S), Oxygen (O), Gold (Au), Palladium (Pd), Copper(Cu), Cobalt (Co), Silver (Ag), and/or Platinum (Pt).
 4. The memorysystem of claim 1, further comprising a word line coupled to the firstcarbon electrode.
 5. The memory system of claim 4, wherein the memorydevice comprises multiple memory stacks.
 6. The memory system of claim5, wherein the multiple memory stacks include memory stacks in multiplevertically arranged decks of memory stacks.
 7. The memory system ofclaim 5, further comprising a dielectric fill material between first andsecond memory stacks of the multiple memory stacks.
 8. The memory systemof claim 6, wherein a first memory stack in a first deck and a secondmemory stack in a second vertically arranged deck are coupled to acommon bit line extending between the first and second decks.
 9. Thememory system of claim 5, wherein a first memory stack in a first deckand a second memory stack in a second vertically arranged deck arecoupled to a common word line extending between the first and seconddecks.
 10. The memory system of claim 1, wherein the controller iscoupled to the memory device over one or more buses communicatingcontrol, address, and data signals.
 11. The memory system of claim 1,wherein the controller is a separate integrated circuit from the memorydevice.
 12. A memory system, comprising: a controller to control thesystem; and a memory device, coupled to the controller, the memorydevice comprising: multiple memory stacks defined in part by arespective sidewalls, such memory stacks each comprising: a firstelectrode; a selector device over the first electrode; a secondelectrode over the selector device; a variable resistance material overthe second electrode; and a third electrode over the variable resistancematerial; wherein at least one of the first, second, and thirdelectrodes comprises carbon; and a sidewall liner material on sidewallsof the multiple memory stacks wherein the sidewall liner comprises anadhesion species; wherein the sidewall liner material is formed by aradio frequency physical vapor deposition (RF PVD) process, such thatthe adhesion species is configured to intermix with the carbon of theone or more electrodes at an interface of the sidewall liner materialand the sidewall of the respective memory stack.
 13. The memory systemof claim 12, wherein the sidewall liner material further comprises adielectric material.
 14. The memory system of claim 12, wherein theadhesion species comprises boron.
 15. The memory system of claim 14,wherein the sidewall liner material comprises boron nitride (BN_(x)).16. The memory system of claim 15, wherein the RF PVD process isperformed in a PVD chamber utilizing a boron nitride (BN_(x)) target.17. The memory system of claim 16, wherein a plasma of a gas comprisingargon is formed in the PVD chamber.
 18. The memory system of claim 12,wherein each of the first, second, and third electrodes is formed ofcarbon.
 19. The memory system of claim 12, wherein the variableresistance material is a phase change material, and wherein the phasechange material comprises one or more of Germanium (Ge), Antimony (Sb),Tellurium (Te), Indium (In), Aluminum (Al), Gallium (Ga), Tin (Sn),Bismuth (Bi), Sulphur (S), Oxygen (O), Gold (Au), Palladium (Pd), Copper(Cu), Cobalt (Co), Silver (Ag), and/or Platinum (Pt).
 20. The memorysystem of claim 12, wherein the selector device comprises one or more ofSelenium (Se), Arsenic (As), Germanium (Ge), Tin (Sn), Tellurium (Te),Silicon (Si), Lead (Pb), Carbon (C), and/or Bismuth (Bi).